Glossary for Fukushima Daiichi crisis
This picture shows the damaged No. 3, left, and No. 4 reactors of Japan's Fukushima Daiichi power plant on Wednesday.
March 16th, 2011
10:41 PM ET

Glossary for Fukushima Daiichi crisis

Workers have been trying to resolve cooling problems at four reactors at northeastern Japan’s Fukushima Daiichi nuclear power plant, whose cooling systems are said to have been disabled by Friday’s tsunami. The crisis has raised serious concerns about radiation.

Below is a short glossary of some terms often used in accounts of the Fukushima Daiichi crisis.

Boiling-water nuclear reactor: The type of nuclear reactor used at the Fukushima Daiichi plant. In these reactors, fuel rods – made of radioactive pellets that usually contain enriched uranium-235 and are encased in zirconium alloy – are placed into a reactor vessel, or large steel tank filled with water. Nuclear fission – the splitting of atoms – is initiated, giving off heat and sending free neutrons toward other atoms, causing more fission in chain reactions. The heat boils the water, which turns to steam. The steam is piped to turbines, making them turn, which creates electricity. A condenser turns the steam back to cool water, which is sent back to the reactor core. See an interactive explaining this reactor type and the Fukushima Daiichi crisis.

Boric acid: A material used to help slow down nuclear fission reactions. South Korea is sending more than 50 tons of boric acid to Japan for use at Tokyo Electric Power's damaged nuclear facilities, Yonhap News Agency reported. South Korea's Ministry of Knowledge Economy said it was supplying the boric acid at Japan’s request after Tokyo used its reserves of the material at the Fukushima Daiichi nuclear plant.

Chernobyl: The site, in northern Ukraine, of the world’s worst nuclear power plant disaster. A meltdown, explosion and fire at the site on April 26, 1986, sent a large radiation cloud over much of Europe and contaminated large areas of then-Soviet Ukraine, Russia and Belarus. Thousands of deaths are said to be attributed to the disaster, and Ukraine's health ministry estimated that one-sixteenth of its population of 49 million was suffering from grave health disorders related to the incident. The disaster led to thousands of cases of childhood thyroid cancer, according to Dr. Ira Helfand of Physicians for Social Responsibility, which opposes the use of nuclear power.

Control rod: A rod, separate from a fuel rod, that contains material that can absorb neutrons. When placed into a reactor, it slows the fission chain reactions. As the control rods are removed, the reactions increase.

Fission: The splitting of an atom, which releases energy - usually in the form of heat - that can be used to produce electricity, according to the U.S. Nuclear Regulatory Commission. To see how the Fukushima Daiichi plant uses fission to produce electricity, see the boiling-water nuclear reactor entry.

Fuel rod: A long, zirconium alloy tube containing radioactive pellets that fuel a nuclear reactor. A group of fuel rods make up a fuel assembly. To see how fuel rods are used at Fukushima Daiichi, see the boiling-water nuclear reactor entry.

International Atomic Energy Agency (IAEA): This agency, with 151 member states, inspects nuclear and related facilities under safeguard agreements. It was established in 1957 to facilitate the peaceful use of nuclear energy. Among other things, the agency monitors nuclear reactors to make sure nuclear material is not being diverted for making weapons, and it helps countries prepare and respond to emergencies.

International Nuclear and Radiological Event Scale (INES): A scale developed by the IAEA to identify the severity of nuclear incidents. It goes from level 1, which indicates very little danger to the general population, to level 7, a "major accident" with a large release of radioactive material and widespread health and environmental effects.

Japanese nuclear authorities initially rated the Fukushima Daiichi incident at level 4, which is characterized as a minor release of radioactive material that necessitates only measures to control food due to contamination. But Joseph Cirincione, president of the Ploughshares Fund and author of "Deadly Arsenals: Nuclear, Biological and Chemical Threats," said the level is far beyond 4. "We are way beyond Three Mile Island level and heading into Chernobyl territory," he said. "This is at least a 5, probably a 6 (a serious accident) and it could end up a 7."

"It's clear we are at level 6, that's to say we're at a level in between what happened at Three Mile Island and Chernobyl," Andre-Claude Lacoste, president of France's nuclear safety authority, told reporters Tuesday.

Level 6 events have broad consequences that require countermeasures to deal with the radioactive contamination. Level 7 events would constitute a larger release of radioactive material and would require further countermeasures.

Meltdown: This refers to the melting of nuclear fuel rods in the reactor core. The melting, which would release radiation from the pellets inside the rods, can happen if the control rods aren’t able to control the chain reactions (and therefore the temperature) inside the core, or if cool water isn’t pumped into the reactor continuously. High temperatures can also compromise the reactor vessel and surrounding containment systems; if those systems are breached, radioactive material could be released into the environment.

At the Fukushima Daiichi plant, three active reactors shut down automatically as intended because of Friday’s earthquake. But cool water still was needed to keep the fuel rods from overheating, and the earthquake caused the water pumps to lose power. Emergency generators then powered the pumps, but the subsequent tsunami damaged those generators. The pumps then operated on battery power, which lasted for eight hours.

Some Fukushima Daiichi reactors are believed to have experienced partial core meltdowns. Tom Cochran, a senior scientist in the nuclear program at the Natural Resources Defense Council, said one uncertainty is whether the reactors’ containment vessels will keep any molten nuclear material from entering the environment. If the containment system is breached, "You have more or less direct access to the environment,” he said. “At that point, you expect the volatile fission products and the gaseous fission products to get out of the system.”

Potassium iodide: A compound that scientists say may give some protection from exposure to radioactive iodine-131, which is one of the fission products that can be released in a meltdown. Potassium iodide would not give any protection against any other radioactive isotope that may be released in a meltdown at a nuclear power plant.

Reactor core: The part of the reactor where the fission takes place. In the case of Fukushima Daiichi plant, it’s the vessel that contains the fuel rods, water and the control rods.

Sievert (and millisievert): A unit of measurement for radiation dosage. According to the World Health Organization, the average person is exposed to about 3 millisieverts a year of radiation, from naturally occurring, medical and other sources. But monitoring at the Fukushima Daiichi site has recorded radiation as high as 400 millisieverts an hour - a level known to be a risk to human health. Exposure to 1,000 millisieverts (1 sievert) of radiation can cause radiation sickness.

Spent nuclear fuel: Nuclear reactor fuel that has been used to the extent that it can no longer effectively sustain a chain reaction, according to the U.S. Nuclear Regulatory Commission.

Spent fuel storage pool: An underwater storage and cooling facility for spent fuel assemblies – groups of fuel rods - that have been removed from a reactor, according to the U.S. Nuclear Regulatory Commission. The water is supposed to cool and shield the spent fuel rods.

On Wednesday, the head of the U.S. Nuclear Regulatory Commission told a House committee hearing that water had disappeared from a spent fuel storage pool in one of Fukushima Daiichi’s units, exposing spent fuel rods and leading to the emission of "extremely high" levels of radiation.

Three Mile Island: A nuclear power plant near Middletown, Pennsylvania, which was the site of the worst nuclear power disaster in the United States. A partial core meltdown occurred in 1979. The plant had containment units, so the release of radioactive material into the environment was minimal. The incident caused no injuries or deaths, and only low levels of radiation were found in plants and animals, experts said.

- CNN's Aaron Brodie contributed to this report.

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Filed under: 2011 tsunami • Japan • Science
soundoff (17 Responses)
  1. Charles

    My empathy with the brave samurai platoon. The absense of duable coolant backup means when dealing with 10,000year fission material is however totally incomprehensible. Next time please call the local fire dept to make the last call with the certification (OR RECERTIFICATION) of nuclear power plants. The local fire dept will most certainly demand (1) a sock for a mobile generator and (2) quick-couple means for an external pumping resource. However the engineers, contractor and regulatory agencies should be held fully accountable for the Daiichi mess.

    March 17, 2011 at 12:46 am | Report abuse |
    • Idaho Tom

      I say, we shouldn't be pointing fingers and blaming people. The three back-ups failing was not something anyone was able to intelligently assess a practical probability. It's not just blindly saying it will or won't happen. There are complicated risk assessment procedures that are used to assess the probability and it was in all practical means, impossible to happen. It did happen, but its like saying, there's a finite possibility for a plane to crash, literally a one in 7 million flights. That's virtually an unthinkable number for every practical means so everyone flies even though THERE IS the finite risk but doesn't mean that that risk is always preventable and because of that, we should fly. Sometimes, there's just straight bad luck from statistics. We can keep on adding quadruple, octuple, 20 redundant systems, but still a finite risk of failing.

      Sure they WILL be held accountable and many people will be fired, but that doesn't mean that those who are accountable should be treated like devils/criminals. It's because those who will take responsible and be held accountable that people can actually build and run reactors/power plants/dam/wind farm and get electricity to power their computers and type messages from their comfortable air-conditioned, warm/cool house with pop-corn or meal cooking in their stoves/micro-waves, watching their televisions and doing everything they are with electricity.

      It'll be very beneficial for the general public to understand how many billions of dollars are required, how much responsibility the managers have to take and the whole system management. I'm an engineer that does the technical work, but I sure am glad for the managers that has to manage us, manage a project by a certain dead-line and if not, get fired, or be held accountable in case of something that they had no practical control over like this case.

      March 17, 2011 at 2:24 am | Report abuse |
    • EveryOneLoses

      Nuclear Energy has now been shown to be unsafe in the modern era of earthquakes greater than 6.0, which most facilities have only been built to withstand. There are even some nuclear power plants built on or near earthquake fault lines, which should be immediatly assessed for shutdown commencement, if our government is prudent. This matter is serious inasmuch as we now know that it takes months for a depleted fuel rod storage pool to cool to safe levels, let alone a running reactor that scrams at the time of an earth quake event. Take no chances, begin now in closing these plants located on faults in America, the citizens should demand it.

      March 17, 2011 at 3:38 am | Report abuse |
  2. OK

    So turn it on and let the condenser cool the thing down

    March 17, 2011 at 1:15 am | Report abuse |
  3. ad

    is it practically possible now to cool the residual heat of the order of 2000s of degrees in the nuclear fuel rods in the reactor and spent fuel reactor rods in pool???

    March 17, 2011 at 1:29 am | Report abuse |
  4. Randall Bart

    You should mention that "sievert" is the newfangled word which replaced "rem", which in its time was the newfangled word which replaced "rad". I think they changed the word so that we can all feel ignorant.

    March 17, 2011 at 1:54 am | Report abuse |
  5. Arvin

    this is why we should not use nuclear power

    March 17, 2011 at 2:03 am | Report abuse |
    • guy

      Arvin what should we use coal. nataral gas, solar, wind? You see the problem with the first two is they, will not last forever.Coal is hard on the envoriment and become more and more expensive. Nataral gas used to make electricity on a massive scale is already on the expensive side. The last two do not have the capacity. For all you friends of earth and hippie folk. Let me get this down to a third grade level. If we start building solar panels and wind turbines today. Building 24 hours a day for the next year. We still would not have the capacity from these renewable energy. Plus the land useage issue. Im not against these energy soruces,and neither is the electric utilities. Fuel cost for the soruces would be cheap like free. If you can take nothing and sell it for something. PURE PROFIT what company would not jump on this like a fat kid on a cupcake. Friends of earth shut the coal and nuclear plants. Will have black outs and brown outs. Cold showers, No Charlie Sheen crazy moments on you tube, and no cold beer. We are just addict to electricity as we are oil.

      March 17, 2011 at 6:23 am | Report abuse |
  6. anonymuf

    criticality [ˌkrɪtɪˈkælɪtɪ] n. (Physics / Nuclear Physics) the condition in a nuclear reactor when the fissionable material can sustain a chain reaction by itself

    A criticality accident, sometimes referred to as an excursion or a power excursion, is an accidental nuclear chain reaction in a fissile material, such as enriched uranium or plutonium. ...

    March 17, 2011 at 2:35 am | Report abuse |
  7. GH

    Thank you. What about the consequences of plutonium release from the mox mixture? What could be done to mimimize exposure and health consequences to these " any other radioactive isotope that may be released in a meltdown at a nuclear power plant" and what are we talking about here besides Cesium, Iodine, and Plutonium? And what scale of contamination may be expected in response to different potential outcomes .. ie complete meltdown coupled with full containment breach in one and or all of these six reactors? Any additional info would be greatly appreciated.

    March 17, 2011 at 2:36 am | Report abuse |
  8. anonymuf

    decay heat (di′kā ′hēt)
    (nucleonics) Heat produced by the decay of radioactive nuclides.

    Decay heat is the heat produced by the decay of radioactive fission products after a nuclear reactor has been shut down. Decay heat is the principal reason of safety concern in Light Water Reactors (LWR). It is the source of 60% of radioactive release risk worldwide.

    March 17, 2011 at 3:28 am | Report abuse |
  9. Aladár Stolmár

    A few of us, nuclear engineers were, are fighting for lifetime for the consideration of real processes in the reactor severe accidents.

    As I formulated in a comment to US NRC: Consideration of the zirconium-steam reaction and the ignition and intense firestorm in nuclear reactor fuel rods is well overdue. Reevaluating the evidence provided by the TMI-2 reactor accident, Chernobyl-4 reactor accident, and Paks Unit 2 fuel washing incident, with consideration of this intense fiery process, will bring us closer to an ultimately safe nuclear power plant design.

    Also, I called two years ago for a review: If the hydrogen which is generated in the reactor core from the reaction of the steam (coolant) with the zirconium alloy (or other low neutron absorbing metal cladding and other fuel bundle elements) explodes inside the building surrounding the reactor, this detonation still will not cause a break of the pressure boundary of the containment.
    Thirty years after the TMI-2 accident and 23 years after the Chernobyl disaster, I feel obligated to formulate this guideline in order to protect the public from further irradiation from the use of nuclear power. The Chernobyl type reactors (RBMK), which are still operating, have to be shut down immediately because they do not satisfy this guideline. Other nuclear reactors operating and future designs shall be reviewed for compliance to this key requirement and the result of such review shall be defining for their future.

    Returning to the comment to US NRC : „It is a much overdue duty of NRC and IAEA to evaluate the evidence provided by the TMI-2 accident, Chernobyl-4 accident, Paks-2 incident, and related experiments. Evaluating this evidence, one can see that the ignition of the zirconium fire in the steam occurs at a local temperature of the fuel cladding of around 1000-1200'C, [[and that a self-feeding with steam due to the precipitation of eroded fuel pellets and zirconia reaction product from the hydrogen stream into the water pool, causes intense evaporation.]]
    There are insignificant differences in the progression of the firestorms that occurred in the TMI-2 reactor severe accident, Paks washing vessel incident, and Chernobyl-4 reactor accident; the later defined only by the amount of zirconium available for the reaction. At the mean time, there are significant similarities in the processes leading to the ignition of the firestorm. In all three of the compared cases, it took several hours of ill-fated actions or in-actions of the operators to cause the ignition condition. Also, there are similarities in the end result of the firestorm; namely, that the extent of the fuel damage is much less than it was predicted from any other severe fuel damage causing scenarios, introduced for explanations. Therefore the fraction of released fission products is significantly less than was anticipated from the fuel melting or a so called "steam explosion" scenario. Also, the fiery steam-zirconium reaction results in a much higher than anticipated (from any other scenarios) rate of Hydrogen production, which in turn requires a review of containment designs.”

    I hope You will find useful this information for the background of the Fukushima Daiichi plant recent events.

    March 17, 2011 at 4:54 am | Report abuse |
  10. ZZ Top

    Superman, we need you!

    March 17, 2011 at 6:08 am | Report abuse |
  11. cbonner

    The difference between "radiation" and "contamination."

    March 17, 2011 at 7:23 am | Report abuse |
  12. Sarah

    May God be with us all.

    March 17, 2011 at 10:53 am | Report abuse |
  13. Krissy

    Nuclear power is not worth the trouble. I would rather break out the sleeping bag and candles than end up with cancer. Man wont stop til all the earth is trashed.

    March 17, 2011 at 4:03 pm | Report abuse |
  14. KHAN

    Our Prayers for you

    March 18, 2011 at 11:17 am | Report abuse |